Comet C/2023 A3 (Tsuchinshan-ATLAS)

Click on photo for larger image.

Comets are balls of ice, rocks, frozen carbon dioxide, carbon monoxide, ammonia, and methane. They are thought to mostly reside in a region called the Oort cloud, a distant collection of small objects orbiting the sun 2,000 to 200,000 times farther from the sun than is the earth. A gravitational perturbation occasionally knocks one of these objects into an orbit that enters the inner solar system. Such an event produced comet C/2023 A3 (Tsuchinshan-ATLAS), photographed here shortly after it passed by the sun in September 2024.

Radiation from the sun vaporizes some of the comet and the solar wind blows the debris outward, producing the characteristic tail. Just visible in this photo is also the "anti-tail" formed by heavier particles knocked loose from the comet that orbit behind its path.

The comet is named for the year of its discovery and the two observatories that first identified it. The Tsuchinshan (Purple Mountain) Observatory is in China. ATLAS (Asteroid Terrestrial-impact Last Alert System) is a network of observatories; the site in South Africa shared in the discovery.

Whether this comet is in a periodic orbit or is on a path leading to ejection from the solar system is not currently known.

The field-of-view in this photograph is 9.4 x 6.4 degrees. For comparison, the angular size of the moon in the sky is 0.5 degrees. A video showing a close-up view of the motion of the comet's head is here.

Craig Lent, 31 minutes, ZWO ASI2600 pro, Rokinon 135mm FL lens @ f/2.0
Potawatomi Wildlife Park, Marshall County, Indiana